The present invention relates to a flow matching device and more particularly to a check valve structure facilitating simplified control of a hydraulic actuator.
As is understood by those skilled in the art, large process control valves, e.g. such as those employed in petroleum refineries and chemical and power plants are often driven by electrically controllable, hydraulic positioning systems. Such hydraulic positioning systems commonly includes a powerful, single-acting, spring-return hydraulic piston and a constant speed positive displacement pump which provides a source of hydraulic power, both for stroking the piston and for holding same at any selected position within its stroke. Typically the pump is run continuously and the pressure to the actuator is modulated by a convential three way servo valve or equivalent systems means such as a flapper nozzle or jet pipe system which relieve excess pressure to the sump. The servo valve, in turn, is responsive to an electrical command signal employed in conjunction with a position feedback loop.
While the actuator is immobile, the servo valve throttles the pump output in order to create the proper back pressure as required to hold the piston in position and the totality of the flow is returned to the pump sump when the piston is immobile. As a result of the continuous pump operation, the efficiency of present state-of-the-art hydraulic actuators system is, in the large majority of applications, in the order of five percent or less. Inherently a majority of the hydraulic energy generated by the pump is wasted as heat while the actuator is immobile at any intermediate positions. As is, in fact, immobile much of the time in most valve applications, particularly in large and rather stable processes. Not only is the loss of energy wasteful, the heat created is itself troublesome.
Among the several objects of the present invention may be noted the provision of a reciprocative check valve which selectively allows free flow through a single line port in either direction in order to selectively fill or unfill a variable volume load, e.g. to extend or retract the piston of a single-acting, spring-return actuator; the provision of such a reciprocative check valve which maintains the piston positions's volume with a single positive acting check valve when the piston is immobile; the provision of such a reciprocative check valve which adjusts the flow returning from the actuator to the flow from the hydraulic power source; the provision of electro hydraulic actuator in which the pump need be operated only when the piston is moving; the provision of such an actuator in which the piston position's volume is maintained by positive acting check valves when the piston is immobile; the provision of such a system which may be precisely controlled; the provision of such a system which has a symmetrical response; the provision of such a system which is reliable and which is of relatively simple and inexpensive construction. Other objects and features will be in part apparent and, in part, pointed out hereinafter.